1. Field of the Invention
This invention relates generally to switching circuits and, more particularly, to a digital switching circuit for providing control of a load or loads coupled thereto in response to selective input signals.
2. Prior Art
There are many applications where a switching circuit allows a user to control the operation of a load. For instance, many households utilize two-speed alternating current electric motors for performing different tasks. For example, many of today's cooking stoves have associated therewith a venting hood positioned over the range top. This venting hood usually includes a lamp and a two-speed AC motor for driving a fan so as to vent steam and cooking odors to the outside atmosphere. Typically, the motor speed or RPM is controlled by a single push-button switch built into the hood which is depressed by the user to control the connection of the motor windings so as to vary the speed of the motor. Most, if not all, of these type of switches utilized today require the user to sequence the operation of the motor in a predetermined manner. Thus, the motor can only be switched from an "off" mode of operation to a first speed of operation by manually closing a set of switch contacts. To switch the motor to a second speed of operation, the switch must again be closed. Finally, the motor is turned off by manually depressing the switch a third time. Thus, it is not possible for the user to directly select the speed of operation of the motor between a low or high speed from an "off" mode without first switching the motor to the first speed and then switching it to the second speed. Moreover, if the motor is running at the first speed, the user cannot directly turn the motor off but must first switch the motor to the second speed and then depress the switch again to turn the motor off. This type of sequential switching is undesirable.
Thus, there is a need for a compact switching unit which can provide multiple output signals for controlling the connection of a plurality of appliances to control the operation thereof and which permits the user to directly select a desired mode of operation.